<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

</head>
<body>
<h1>元素A</h1>

<hero>元素B</hero>

</body>

<!--script-->
<script>document.createElement("hero")</script>
<style>
    hero {
        display: block;
        background-color: #4e555b;
        padding: 50px;
        font-size: 30px;
    }
</style>
</html>